The aim of these investigative studies is the continuation of research on various aspects of viral carcinogenesis with special reference to simian virus 40 (SV40). This undertaking has been pursued by the Principal Investigator for the past 16 years (1963-1979). In the immediate future he will use lymphocytic malignant neoplasms that he has induced in hamsters by SV40, to identify the cell-mediated and host-mediated factors that determine the pathogenesis of neoplastic lymphocytes in the immunocompetent host. In particular, he will atempt to discover the conditions under which such cells may behave either as generalized leukemia, which is associated with poor prognosis, or as localized lymphoma, which is associated with favorable prognosis. This animal model, which resembles very closely the analogous human lymphocytic neoplasms, can serve as a means to elucidate the factors responsible for the differences in behavior noted between leukemia and lymphoma in humans.